Only getting 5 volts on passenger side headlights. Topic is solved

[Luke.T5R]

Just as the title says, on my passenger side headlights both terminals in the 3 terminal plugs read 5vs with the key on, with my negative prong in the third pin in the connector. The Drivers side reads a full 12 and works perfectly, obviously my passenger side does not work on either high or low beam. I have a parts car and have tried a new switch, I do not see any obvious damage on the wiring coming from the harness. I have also tried 3 different headlight housings all with working bulbs. The only thing i haven't tried just swapping is the headlight relay under the fuse box. Is this a common issue? anyone ever had a similar problem? Thanks.

[scot850]

Have you got a bad ground on that wiring for the headlight?

Neil.

[Luke.T5R]

Have you got a bad ground on that wiring for the headlight?

Neil.

that was my initial suspect but i do not see anything obvious. all engine ground straps are intact in the rear and the main on the front on the transmission is on and good. harness going to the plug looks good and the plug looks brand new.

[RickHaleParker]

5V drop to chassis ground or some other reference?
What is the voltage drop across the bulb?

[Luke.T5R]

5V drop to chassis ground or some other reference?
What is the voltage drop across the bulb?

I am not an electrician so pictures might do better to illustrate what im seeing. This is what I get on the passenger side plug coming from the body of the car

This is what I see on the drivers side plug coming from the body.

Both have the same readings to the actual plugs within the headlight housing. I have replaced the headlight switch and the relay, both creating the same issue. Only thing I haven't plugged in just to try is the stalk, but i do have one on my parts car so I could give that a shot as well.

Like i said im not an electrician so if there are different tests I can try or maybe something obvious I'm missing.

[BEJinFbk]

What do you see using the battery as your ground?

[RickHaleParker]

Put the black (-) lead on the battery post (-) and leave it there as you take three measurements with the read lead ( + ) by moving the red lead only.

• 1. Across battery.
  2. ( + ) On the passenger side connector.
  3. ( - ) On the passenger side connector.

4. How move the black lead and take the same reading you did before ( 5V last time ).
Post the four readings.

From that we should be able to tell which side the voltage drop is on and how much.

[Luke.T5R]

Okay thank you to both of you I will check that when I get home from work tomorrow! I will post those readings tomorrow afternoon

[Luke.T5R]

Okay, so I did what was suggested and came up with essentially the same results. on the 2 of the pins read 5 volts with the negative lead on the negative battery post. On the functioning side I got almost full battery voltage, about 11.5vs testing the same way. I don't know if this is relevant but I measured resistance between the ground plug and the battery post and couldn't get my meter to read any resistance no matter what range i put it in. This was the same on both sides.

EDIT: Sorry today at work was a lot and i re read the post and here are the measurements you guys requested
1. 12.49V
2. 5.06V
3. 37mV
4. 5V

[RickHaleParker]

EDIT: Sorry today at work was a lot and i re read the post and here are the measurements you guys requested
1. 12.49V
2. 5.06V
3. 37mV
4. 5V

Put it back together. Turn on the headlights.
Black lead back on battery. Measure voltage each side of Fuses F21 & F22 under the hood. Four measurements in total.
Swap fuses F21 & F22 see if the problem moves to the other side.

Possible sources:
1. Bad connection, Current limiting resistors or Relay contacts in the Central Electrical Unit.
2. The common ground at the headlight connector has a high resistance to ground.